This invention relates generally to rotary devices. More specifically, this invention relates to outer envelope trochoidal rotary devices.
Trochoidal rotary devices are constructed so that a rotor assembly planetarily rotates in a housing defining a cavity. Trochoidal rotary devices can be divided into two groups: inner envelope trochoidal devices; and outer envelope trochoidal devices. In an inner envelope trochoidal device, the rotor assembly includes apex seals that cooperate with the inner wall surface of the housing to define a plurality of discrete chambers. In an outer envelope trochoidal device, the apex seals are mounted in the inner wall of the housing between individual working chambers. The peripheral surface of the rotor assembly cooperates with the apex seals to define a plurality of discrete chambers. Accordingly, the rotor assembly of an outer envelope trochoidal device functions, in part, to seal off the working chambers of the device. The peripheral surface of the rotor assembly and inner wall of the housing function as working chambers for expansion engines, compressors, expanders, meters, etc.
In an outer envelope trochoidal device, because the peripheral surface of the rotor assembly cooperates with the apex seals of the inner housing to provide a working chamber, it is necessary for the peripheral surface of the rotor assembly to have a construction that will create a seal between the rotor assembly surface and the apex seal. If a seal is not created between the apex seal and peripheral surface of the rotor assembly, the efficiency of the engine or compressor will suffer.
In order to ensure that the rotor assembly planetates correctly in the rotor housing, the rotor assembly must be balanced. Typically, rotor assemblies are balanced by counterweights that are located outside the rotor on the shaft that planetates the rotor assembly. Although it is possible to balance the rotor assembly with these counterweights, it is usually difficult to make the fine balancing adjustments that may be needed.
In a single-piece cast rotor, requiring a sand core, it is not possible to locate the casing in the machining process such that the finished wall thicknesses are all identical. This means that it is literally impossible to machine the casting in such a way that it is reasonably balanced. Since the sides and the periphery of the casting must be essentially smooth, with no interruptions that would cause seal collisions, there is very little surface on the outside of the casting available for removing material to balance it. A two-piece casting would be desireable since the casting can be made without coring, and it is possible to locate the casting in the lathe such that the finished wall thicknesses are identical, thus minimizing the amount of balancing necessary in the finished rotor.
Furthermore, it is desireable for the rotor assembly to be easily disassembled. For example, if a two piece rotor assembly were developed, it would be advantageous if it were easily disassembled so that the bearings could be easily removed for maintenance and repair.
Accordingly, there is a need for an improved rotor for an outer envelope trochoidal device.